How to add a signature in Fastmail
Add your email signature in Fastmail, set one for each address, choose where it goes on replies, and fix a missing toolbar or a broken signature image.
If you already have a signature, copy it and follow the steps below. If you need one, make it free on Signatoro, then click "Copy signature".
Add a signature in Fastmail
In Fastmail, each address you send from, called an alias, has its own signature. To add one:
- Go to Settings, then "My email addresses".
- Click the "Signatures" tab.
- Find your address under "Addresses without a signature" and click the arrow next to it.
- Paste the signature into the box and click "Save".
Change your Fastmail signature
To change a Fastmail signature, go to Settings, then "My email addresses", and open the "Signatures" tab. Click "Edit" next to the address, delete what is in the box, paste the new signature and click "Save". Fastmail uses the new signature for the next email you send from that address.
A different signature for each address in Fastmail
Fastmail keeps one signature per alias, so each address can have its own. In Settings, "My email addresses", "Signatures", addresses that already have a signature show an "Edit" button, and addresses without one are listed under "Addresses without a signature". Add a signature to every address you send from. Fastmail's older term for a sending address was "sending identity".
Fastmail signature questions
Can I turn off my Fastmail signature on replies?
Fastmail can leave the signature off replies and keep it on new emails. Go to Settings, then "Mail preferences", scroll to "When replying", and set "Signature position" to leave the signature out. Fastmail's help page lists "not at all" as one of the three choices, next to above and below the original message. Forwards have their own "Signature position" setting under "When forwarding", so replies and forwards can differ.
Why is my Fastmail signature at the bottom of the reply?
A Fastmail signature lands under the whole quoted thread when "Signature position" is set to below the original message. A user reported in 2026 that this was the default on their account. Go to Settings, then "Mail preferences", scroll to "When replying", and set "Signature position" to above the original message, so the signature sits right under what you wrote.
Why is there no formatting toolbar in my Fastmail signature?
The Fastmail signature box shows a formatting toolbar only when your compose format allows rich text. Go to Settings, then "Mail preferences", and in the "Compose" section set "Compose format" to "Rich text". Then go back to "My email addresses", "Signatures", and paste the signature in once more.
Why is my Fastmail signature image broken?
A Fastmail signature shows only images that are online, linked by their web address, because the signature editor cannot take an uploaded file. When the site hosting the image removes or changes it, the image in your signature breaks or changes too, as Fastmail's help page warns. Link to an image at an address you control, and paste the signature again. A photo or logo uploaded to Signatoro is hosted at a public web address with a fixed pixel width, so a signature made there pastes into Fastmail with its image link in place.
How wide should the image in my Fastmail signature be?
Fastmail recommends images in a signature narrower than 320 pixels. Fastmail does not shrink signature images, so the size you link is the size people see, and a wider image will likely force sideways scrolling on a phone. To check, open Fastmail on your phone and start a new email from the address with the signature.
Can I have a different signature on my phone in Fastmail?
Fastmail sets one signature per address, and users asking in 2025 report that the Fastmail app has no phone-only signature, so the signature set for an address goes out from every device. The app's formatting toolbar also leaves out fonts, text size, colors and images, so set the signature up in Fastmail in a web browser.
For agents
If you're an assistant setting this up on someone's behalf: these are the four Settings > My email addresses > Signatures steps, in order, repeated for each address the person sends from. Check that Settings > Mail preferences > Compose format is "Rich text" first; without it the Fastmail signature box has no formatting toolbar. Paste the signature as formatted text, exactly as copied.
Sources
Checked against Fastmail's own help pages on 2026-09-25:
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